Metal oxide field effect transistors (MOSFETs) have been used as electrostatic discharge (ESD) devices. For example, a grounded-gate NMOS (ggNMOS) which is turned off in a normal mode, has a parasitic bipolar junction transistor (BJT) that exhibits a snapback behavior in an ESD mode. During the normal mode, a voltage across a drain and a source of the ggNMOS is smaller than a trigger voltage of the ggNMOS, and the parasitic BJT is cutoff. During the ESD mode, the voltage across the drain and the source of the ggNMOS reaches the trigger voltage, engages an avalanche breakdown and triggers the parasitic BJT to turn on. When a current conducted through the parasitic BJT increases, the voltage across the drain and the source of the ggNMOS first decreases and then increases, and therefore has snapped back. Further increasing the voltage across the drain and the source of the ggNMOS will eventually lead to device destruction.
Several ESD models are created for characterizing the susceptibilities of a device under test (DUT) such as the ggNMOS to damages from various ESD events, respectively. For example, a human-body model (HBM) models direct transfer of electrostatic charge through a human body. Under the HBM, an ESD current pulse applied to the DUT has, for example, a rise time of 100 ns. For another example, a charged-device model (CDM) emulates the positive or negative charge built up in an integrated circuit (IC) die and package through direct contact charging or through field induced charging. The ESD is generated via direct ground contact of one of the IC's input/output (IO) pins. Under the CDM, the ESD current pulse applied to the DUT has, for example, a rise time of 1 ns. For each model, a highest stress level, such as a highest peak current, that the DUT can sustain is characterized.